This invention relates to HID mercury-vapor lamps and, more particularly, to such a lamp which utilizes a particular phosphor combination in order that the visible output and appearance of the lamp are substantially color corrected in all respects.
High-pressure, mercury-vapor (HPMV) lamps are extensively used for lighting highways, parking lots, high-bay factories and similar applications. The visible emissions from such a lamp, when they are not otherwise corrected with respect to its color, are concentrated primarily in the green and yellow and violet regions of the visible spectrum. Such lamps have been color-corrected for many years by utilizing a coating of red-fluorescent phosphor material on the inner surface of the outer envelope, in order to utilize the otherwise wasted ultraviolet radiations which are generated by the arc. The first practical embodiment of such a lamp is described in U.S. Pat. No. 2,748,303, dated May 29, 1956. A modification of such a color-corrected lamp utilized yttrium vanadate activated by trivalent europium or yttrium phosphate vanadate activated by trivalent europium for purposes of color correction. With such a lamp, there still existed an excessive amount of yellow radiations from the mercury arc and in order to compensate for the excess of yellow radiations, U.S. Pat. No. 3,670,194 dated June 13, 1972 disclosed adding to the red-emitting phosphor component a limited amount of narrow blue-emitting phosphor. The resulting composite lamp emission provided good color rendering of illuminated objects. The emission color of the lamp, however, normally fell somewhat below the so-called black body line, which caused the lamp to have a purplish hue.
It is known that good color rendering of illuminated objects can be obtained with three selected narrow bands or lines of radiations, as taught in U.S. Pat. No. 4,176,299, dated Nov. 27, 1979.
The internationally accepted method for standardizing and measuring the color rendering properties of light sources is set forth in a publication of the International Commission on Illumination identified as Publication C.I.E. No. 13 (E-1.3.2) 1965.